Not everyone here speaks/writes the same language. To help with communication, please categorize yourselves by language categories on your user page. Example language groups: en for English, de for German, and so on. Additionally, users can specify their level of proficiency in the language:

0 indicates someone who does not understand the language.

1 stands for basic knowledge: the ability to understand and answer simple questions in the language.

2 stands for intermediate knowledge.

3 stands for advanced or fluent knowledge: the ability to correct spelling and grammar errors in the language.

4 stands for near-native ability.

N stands for native language.

So de-1 identifies a user with basic skills in German, and en-3 identifies a user with advanced skills in English.

The two-letter language codes are the same codes described in ISO 639, while the number roughly corresponds to the ILR scale (though this is coincidental). The three letter codes do not always conform to the ISO standard, though. There can also be weird bracket codes like "el(a)", which likely cannot be deciphered by people that don't speak this language. (See the complete list of language Wikipedias available).

Note: Level 0 is less often used, because it is assumed that users do not understand languages if they don't list them with one of the other levels. However, it can be useful on some multi-lingual wikis, to advise that you do not speak an expected language – for instance, you may be able to contribute to a wiki without speaking a language (adding links or pictures, say).